1. Field of the Invention
The invention in general relates to hydraulic liquid supplies, and more particularly, to an arrangement used in the underwater environment and wherein liquidborne noise is minimized.
2. Background Information
Liquidborne noise from hydraulic pumps is a major, and objectionable noise source in underwater systems such as submersible vehicles. In operation, hydraulic pumps excite the structure to which they are attached, they excite the surrounding medium and they excite the hydraulic liquid being pumped.
Structural excitation may be reduced by the use of isolation mountings and direct excitation of the surrounding ambient medium is reduced by the gas within the pressure vessel which provides a large acoustic transmission drop. Several techniques exist for reducing liquidborne noise including the use of an accumulator to smooth out hydraulic pulsations, as well as the use of mufflers and flexible hoses. None of these techniques, however, provide sufficient quieting, and noise generated within the hydraulic pump travels through the hydraulic lines such that it radiates to the surrounding ambient medium through the hydraulic tubing walls as well as a load (if utilized) being supplied with the hydraulic liquid.
The present invention provides for an improved arrangement for reducing liquidborne noise from the hydraulic pump.